Looking at the recent Android beta, the text here implies to me that it’ll be a (small?) core charge then users will be able to select add-ons:
This is what @nexusmaniac found in the Android Tear Downs and Deep Dive thread:
<string name="premium_subscription_intro_body">You can now get these exclusive add-ons for just %s a month, with the option to pay more for extras like travel insurance.</string>
<string name="premium_subscription_intro_title">"Get even more from
your Monzo experience"</string>
<string name="premium_subscription_intro_toolbar_title">Monzo Plus</string>
If the code extract is difficult to read, here’s the relevant bit pulled out:
You can now get these exclusive add-ons for just %s a month, with the option to pay more for extras like travel insurance.
The %s is a variable which means that Monzo can change it without having to change the text in the app. It also means they can hide it from @nexusmaniac until they’re ready to launch 