Many apologies! We are working right now to improve the email invitation feature and prevent you from having and difficulties. In the meantime, our guess is that you probably have an extra space at the beginning of the email address or at the end of the address. This happens a lot when copying and pasting email addresses. Make sure all extra spaces are removed and that the cursor is abutting the last letter in the address. The "Send" button should appear with these steps.
Hope this helps!
Oliver @ SelectivorSelectivor is how we eat together.