You are trying to add multiple forms to the same page. For example, you add two donation form parts to the same page. You may add a donation form part and an event form part to the same page. When users try to submit or continue on the form, they are prompting with an error message. The error may indicate a required field is missing, even though the user filled out the required field.
Multiple forms on the same page will cause errors when trying to submit the form. Multiple forms cannot be added to the same page. Each form will have to be placed on its own page. As a general rule, only one part with a Continue or Submit button is allowed on one page at a time.