The Teamup app uses the web-based login forms. A recent user report brought to our attention an issue that might happen with the iOS app: If you "get stuck" on the login form, check the mobile browser settings.
If you have the mobile browser set to "Block all cookies," turn this setting off and try to log in again. (Once logged in, you can turn the setting to block cookies back on again.)
For example, if you're using Safari as your mobile browser, the steps would be:
Other mobile browsers may have different steps. If you're using Vivaldi, for example: