Strictly, a joint venture is two parties agreeing in writing to work one specific deal together, defining who does what and how the proceeds split. In wholesaling that usually means one partner handles acquisition (finding the motivated seller, signing the purchase contract) and the other handles disposition (bringing the end buyer), with a signed JV agreement naming the property and the split.
The loose market usage is what you ran into. People say "I JV'd that" about anything from a full written partnership down to texting an address to someone for a tip, which is closer to bird-dogging, being paid a finder's fee for a lead. Those are different animals, and whether you can legally be paid a fee for producing a buyer or a lead when you have no contractual interest in the property depends on your state's brokerage rules, so ask a licensed attorney in your state before you take money that way.
On signatures: usually one partner is the buyer on the purchase agreement with the seller. That person is the one the seller can enforce against, and that person is also the assignor when the contract is assigned to the end buyer. The partner not on the contract gets paid at closing, typically by having both partners sign a joint instruction to the closing agent so the fee is split on the settlement statement and each gets a check directly.
Get that instruction signed early. If your partner is on the paperwork and you're relying on them to pay you after they receive the whole fee, you have a promise rather than a mechanism, and closing agents differ by state and by company on whether they'll cut two checks at all.
