Formitize has a spam filter in place, which will stop an email from sending if the filter comes across something in the email message that has a high chance of being caught in receivers' spam folders when being sent to them.
Sometimes this can be something like terms and conditions that have been set up in the quote or invoice settings. There are some phrases or words that will be picked up by email spam filters and the Formitize filter is there to pick up on them based on what might be sorted into a customer's spam if it does send.
You can also review and / or change your invoice or quote settings in the Web Portal by going to the Settings cog > Accounts > Invoices or Quotes.
In the App, go to Settings cog > Invoices or Quotes.