Critical Error

I’m pretty sure this is a server problem rather than a CoCart problem, but I’m stumped. I am getting the default WordPress critical error message when I try to add products by ajax using CoCart Lite 3.0.12 with WordPress 5.8 and WooCommerce 5.5.2. Unfortunately, I can’t link to the page because it has a server level password.

Here is the responseJSON object:

{
“code”: “internal_server_error”,
“message”: “<p>There has been a critical error on this website.</p><p>Learn more about troubleshooting WordPress.</p>”,
“data”: {
“status”: 500
},
“additional_errors”: []
}

Here is the data submitted to /wp-json/cocart/v2/cart/add-item:
{
“id”: “20”,
“quantity”: “1”,
“item_data”: {
“clspm_delivery_date”: “Saturday, August 21, 2021”,
“clspm_delivery_time”: “12:00 pm”
}
}

If browse to /wp-json/cocart/v2/cart/items, this is what I see:

<b>Fatal error</b>: Allowed memory size of 268435456 bytes exhausted (tried to allocate 20480 bytes) in <b>/home/hlwmfvqp/public_html/wp-includes/wp-db.php</b> on line <b>1370</b><br />
<br />
<b>Fatal error</b>: Allowed memory size of 268435456 bytes exhausted (tried to allocate 20480 bytes) in <b>/home/hlwmfvqp/public_html/wp-includes/class-wp-fatal-error-handler.php</b> on line <b>72</b><br />

I can add products by ajax from the shop page fine. The same code works fine on two other servers with different themes.

Thanks in advance for any pointers.