SparkPost Dedicated IP problem

Your software
My PHP version is : 8.0.28
My MySQL/MariaDB version is (delete as applicable): 8.0.34

Updating/Installing Errors
I am (delete as applicable): Installing / Updating
Upgrading/installing via (delete as applicable) : Web / Command Line

These errors are showing in the installer :

These errors are showing in the Mautic log :

Your problem
My problem is :

I am using my Mautic system to send via the SparkPost API.
For some reason, it IS sending but it is not sending through the Dedicated IP that I have configured there.
Could you please help and/or advise?

Your help would be greatly appreciated.

Thanks in advance.

Steps to reproduce issue:

Step 1:
Configure Mautic to use the SparkPost API

Step 2:
Send an email through Mautic

Step 3:
Check received email headers and see if it has been sent via the dedicated IP configured on SparkPost

Steps I have tried to fix the problem :

In addition to my initial post, I would like to add that using SMTP instead of API does currently work when adding the following message header:
X-MSYS-API: {“options”: {“ip_pool”: “SPARKPOST_IP_POOL_GOES_HERE”}}

However, this is not the case when trying to use the API.