Pakistani free chat room among all the chatting rooms. The worst part of free software is you get what you get, and the developers don’t have to listen to you. As per cash, we generated $14.6 million in free cash flow in the first quarter driven primarily by higher than expected adjusted EBITDA. As per the second quarter of 2021, our guidance range for revenue is a $112 million to $114 million or 22% to 24% year-over-year. The guidance range for 2021 adjusted EBITDA remains $33.5 million to $41.5 million or 7.3% to 8.9% margin. We closed the quarter with $668 million of cash on the balance sheet, an increase of $14 million from the end of 2020. We’ve continued to strengthen our business we are raising guidance for 2021 revenue from our previous range of $458 million to $466 million to a new range of $460 million to $468 million or a 25.5% to 27.5% growth year-over-year. The New York Times reported on the increase of chatbots in the legal industry, and composed about the factors why chatbots are significantly popular. You can use it when practicing your typing skills to get an idea of how well you are progressing.
Brands can now message social conversations including public and private messages at scale increasing the surface area of automation touch points and the other capabilities when in the Conversational Cloud currently enabling brands to match customer care and social within our platform and our long-term vision to find an engine and social solution for care and marketing powered by AI and automation. Given all of the momentum and an opportunity we continue to experience, we entered Q2 laser focused on retail, e-commerce in sales and marketing use cases, while continue to innovate in customer care. Professional services revenue grew 41% year-over-year and along with that momentum in the B2B, our consumer segment posted record growth of 44% year-over-year. The primary contributors to upstart in the first quarter were overage our demand-based revenue for CPI contracts over performance by our consumer segment and the at-home COVID-19 testing solution that Rob described. We are subject to a number of foreign and domestic laws and regulations that apply to the conduct of business on the Internet and the management of customer and consumer data such as, but not limited to, laws and regulations relating to user privacy, freedom of expression, data privacy, electronic contracts, electronic payment, content and quality of products and services, taxation, advertising, internet neutrality, information, cybersecurity and intellectual property rights.
Convenient and affordable, Smartsupp allows businesses to track and record user sessions on a website, as well as converse with customers. That could boost home testing confidence, create positive user experience and provide the digital enablement that can obviously create an additional level of mitigation in their offices and returning their employees back to office. 3. If you need to refocus your priorities, give back. 100% money back guarantee the library offers next one reference with a distinctive voice and enhance their assistance. I’m really proud of what the team delivered and in privacy our platform has been instrumental in providing additional measures to create a safe working environment for thousands of employees who would feel more comfortable getting back to physical workplace. More than just a help desk, Zendesk Support helps you nurture your customer relationships with personalized, responsive support across any channel. KnowledgeBase is software for lightning-fast customer support and effortless self-service. Please don’t use these licenses, and we urge you to avoid any software that has been released under them. In terms of our reporting segments within total revenue B2B grew 38% year-over-year and hosted software grew 37% year-over-year. Overall seven-figure deal counts increased 400% year-over-year and annual contract values across all market segments increased 120% year-over-year.
Further unpacking the first quarter results and beginning with new logos annual contract values increased more than a 100% year-over-year and four new logos were seven-figure deals. While the new logo growth was led by enterprise, annual contract values were also up significantly year-over-year for new logos across mid-market and small businesses. Our partner network contributed several new logos as well including a seven figure government win, which adds to our momentum in this large target vertical. We materially expanded our reach into large target verticals including healthcare and government where we’re setting our foundation for future growth. We continue to innovate not only in the AI sphere, but also in extending our platform to new channels including social. Billable platform usage continues to accelerate in 2021 and increasing 40% year-over-year and surpassing the high watermark set offset during the fourth quarter’s seasonal peak. Significantly, billable platform volume also continued to accelerate reaching a new high in March, all considered the data clearly signals the recapitalizing on a robust and rapidly growing market for Conversational AI. We also announced a partnership with Medallia offering brands the ability to seamlessly integrate conversations and customer engagement analytics to help them measure and respond to customer employee signals in the real-time.