How can I delete downloaded fonts on my iPhone?

You need to delete the app which is doing this. Look for something with a name like FancyFonts or whatever. Check settings > general > keyboard > keyboards for any odd non-Apple names on the list and remove them.

RR3212 wrote:

In my settings it shows no downloaded fonts.

You can't actually use downloaded fonts in Messages, only in an app like Pages. So what you see must be generated by something else. Does the person you are talking to see that font too?

Which app is this? This doesn't look like a built-in App on an iPhone.

How to Contact an App Developer:

1. In-App Support: Many apps offer an in-app support feature. Look for a "Contact Us" or "Help" section within the app's settings or menu. This may provide you with direct contact information or a form to submit your query.
2. App Store or Website: If you can't find in-app support or need additional assistance, visit the app's page on the respective app store --> How to contact an app developer - Apple Support
3. Email Support: Check if the developer has an official support email address listed on their website or app store page. Send them an email explaining the issue you're facing. Be detailed in describing the problem to receive relevant assistance.
4. Social Media: Some developers maintain active social media profiles. Reach out to them through platforms like Twitter or Facebook, describing your issue or sending them a direct message.
5. Community Forums: Many apps have dedicated user forums or communities where you can ask questions and seek help from other users or the developers themselves.