Franky

A PHP notice like that and your provider is telling you it is due to a php incompatibility? I think you need to consider asking for better support 🙂
Anyway, first:
– this is not related to the RSVP form, but to the cancel form
– the error is also not new, I’ve checked older versions and the error is in those too (I went back till 2021/04/21), probably even before. So I guess you started using the cancel form just recently?

Now the fix (will be in the next version) can be found here:
https://plugins.trac.wordpress.org/changeset/2563106/

You don’t need an extra plugin in EME. Just configure the Stripe settings in EME (and your boleto payment method in it too), and then configure your event to use Stripe as payment method.
The one problem is that you need BRL as currency, which is by default not configured in EME, but can easily be added (I’ll add it for the next version by default). For now, follow this guide to add BRL as currency: https://www.e-dynamics.be/wordpress/hooks-and-filters/ (search for eme_add_currencies as filter).
If you want to add it to the code (and not use a filter), here’s the changeset to add it to EME directly:
https://plugins.trac.wordpress.org/changeset/2562323/

EME can notify people itself (see the newsletter functionality, and also the hooks on event creation), but I have no knowledge about another plugin …

1) Fix is here: https://plugins.trac.wordpress.org/changeset/2558372/
2) You need to configure those extra payment methods in your Stripe dashboard and then configure in EME which of those you want to give to your customers (there’s no API call that lets me get a list of configured payment methods so you need to provide that info).

See the doc on [eme_filterform] :
https://www.e-dynamics.be/wordpress/category/documentation/6-shortcodes/eme_filterform/

I’ve just released a new version for this (because I believe this is not fun for people relying on memberships and page content dripping).

This should fix it:
https://plugins.trac.wordpress.org/changeset/2557009/

Also, check your database table wp_eme_mqueue and see if the mail you wanted to be sent has something filled out in the “attachments” column.