Duplicate functions

Problem/Motivation

I'm replacing SMTP with SendGrid for email delivery on the website. When I'm sending emails, it breaks and I get this error:
Fatal error: Cannot redeclare GuzzleHttp\json_encode() (previously declared in /var/www/html/sites/all/modules/contrib/sendgrid_integration/vendor/guzzlehttp/guzzle/src/functions.php:164) in /var/www/html/sites/all/libraries/mailchimp/vendor/guzzlehttp/guzzle/src/functions.php on line 322.
I need both.

Steps to reproduce

Install SendGrid:

Install the SendGrid module in your Drupal site.
Configure it to send default emails through SendGrid.
Install MailChimp:

Install the MailChimp module in your Drupal site.
Configure it to connect with your MailChimp account.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes