The error that you have is because there is a conflict between Amelia and woo-mailerlite plugin, you can see this plugin as well in the error/screenshot you sent.
Could you please try this fix - (you can save this file on your local machine first as a backup)
comment (or delete) everything in the file functions.php in Amelia plugin which you will find at location:
I have a fatal error to my website and it is saying that it's related to the amelia plugin. Please help.
Hello Sarah Minor,
The error that you have is because there is a conflict between Amelia and woo-mailerlite plugin, you can see this plugin as well in the error/screenshot you sent.
Could you please try this fix - (you can save this file on your local machine first as a backup)
comment (or delete) everything in the file functions.php in Amelia plugin which you will find at location:
wp-content/plugins/ameliabooking/vendor/clue/stream-filter/src/functions.php
just leave <?php at the beginning and then activate Amelia.
Let me know if this helped!