The website encountered an unexpected error. Try again later.

Here's more information on what is not working with this module using both these configs:
Drupal 8.1.31, Give 2.0.0-Beta6
Drupal 10.3.10, Give 2.0.0-Beta6

When you use zeros in the "Interval" fields, the form still defaults to a recurring donation requirement. The note on the config page states that if you use zeros the form can function as a one-time donation... doesn't work

The second and more serious issue is if you remove the Interval lines, you get a white screen of death after submitting the donation form.

I found an ambiguity where a one-off donation AND the first in the list of donation frequencies are both represented as 0 in the donation->recurring column.
My solution is to make the one-off donation -1.
Zeros are no longer allowed in the interval column.
I pushed the solution to HEAD with some related improvements especially in the give form edit form.
I wrote function give_update_10000() to update all the previous donations, however there's no way in the data to distinguish between those one-off donations and the recurring donations which used the first defined recurrence in the GiveForm. So the update assumes that ALL donations with a 'recurring' value of 0 were one-offs.
Can you test and see if the WSOD is resolved?

Get this error now using Drupal Drupal 10.3.10 and Give dev version:
Error: Cannot unset string offsets in Drupal\Core\Field\WidgetBase->extractFormValues() (line 491 of public_html/website/web/core/lib/Drupal/Core/Field/WidgetBase.php).

Please provide more information.
Did you resave the give_form settings on admin/structure/give/
What are those give_form settings?
What values did you put in the donation form?

This is all my developer told me. He did get it working with a modified install.php file. I will attached this file.

I tested an anonymous donation on my machine and it was ok
Your developer should be posting these issues directly.
I can't imagine how a modified install.php file would help, but you didn't attach it...
Please note I'm not the developer of this module, I only patched it up well enough to serve my own purposes.

Are you speaking about the dev version of the Give Module?

What version of Drupal are you using?

Did you use a live credit card and did the transaction go through successfully?

I've been testing with the cheque method on my local machine with the latest dev version. I haven't set up a credit card.
If you ever see the message:
"The website encountered an unexpected error. Try again later."
It means there are more details on admin/reports/dblog, if the database logging module is enabled.