What lessons did you learn from your first API integration project?

I'm working with a small team that's planning its first API integration because our sales, inventory, and customer support systems don't communicate with each other. We've spent too much time entering the same information into multiple platforms, and it's starting to affect productivity. While researching different companies, I came across Inovio Soft, but I'm not looking for promotions or recommendations. I'd really appreciate honest advice from people who have completed similar projects. What challenges surprised you the most, what would you do differently today, and what practical tips can help us avoid common mistakes and delays?

I'm currently planning our first API integration to connect our sales, inventory, and customer support systems. While exploring options, I noticed Inovio Soft, but I'm more interested in learning from others' experiences. In the context of our project install game , the "JJWIN Game" API integration surprised us with its complex authentication process. We'd appreciate practical tips to avoid such challenges.