bbr, glad everything worked out for you. In future leases you might want to specify up front that you will email a copy of your signed and notarized lease (and lease memorandum if they propose using one) but you won’t give them the signed originals until you receive a cashier’s check for the bonus amount.
Since only originals can be recorded that avoids the risk of having the mineral interest tied up and the money never showing up, which has definitely happened.
If the folks doing the leasing won’t agree to that approach you might offer to meet with them in person to exchange your signed originals for their check. It that still isn’t agreeable I’d question whether they are people you want to do business with.