Talk to the businesses you are targeting with the idea. Ask about what their problems are in the area you're looking to solve. Present a potential solution midway through. Ask if you solve their problem and if they’re willing to pay for it. If enough people say yes, get letters of intent and start building it/raising funding for it. If not enough say yes then keep iterating on the customer problems until you find something enough people say yes about.

Do not build a single thing until then (unless you need to do a week or two of R&D to prove out difficult tech you're unsure about). The “if you build it they will come” approach to a B2B startup is mostly a lie. If you’re even moderately close to building something in that much demand, then you’ll have no problem doing the talking.

If you can’t talk then don’t build a B2B startup. If you can’t talk then say goodbye to being able to raise funds for your startup too.

Easier said than done. I’m learning the hard way.