Composer 2.2 gives error on using PHP below 7.3 when it is using 7.3 but shouldnt need it anyway

On CentOS 7 (company boxes so cannot change). Laravel builds stopped working last week with Composer 1. Upgraded to Composer 2.3 and upgraded to PHP 7.3. Began getting the following:

'Connecting to a secure proxy using curl is not supported on PHP versions below 7.3.0.'

Which is confusing because 7.3 is installed and confirmed that composer was using it.

Assumed the issue is actually the CURL version (have 7.29, 7.5 supports secure curl) so installed Composer 2.2 which supports PHP < 7.3.

But now getting the same error: 'Connecting to a secure proxy using curl is not supported on PHP versions below 7.3.0.'

Which is confusing because Composer 2.2 does not require PHP 7.3

Output of composer diagnose:

$ composer diagnose
Checking composer.json: WARNING
require.tymon/jwt-auth : exact version constraints (1.0.0-rc.5) should be avoided if the package follows semantic versioning
Checking platform settings: OK
Checking git settings: OK
Checking http connectivity to packagist: FAIL
[Composer\Downloader\TransportException] Connecting to a secure proxy using curl is not supported on PHP versions below 7.3.0.
Checking https connectivity to packagist: FAIL                                                                                                                                                 
[Composer\Downloader\TransportException] Connecting to a secure proxy using curl is not supported on PHP versions below 7.3.0.                                                                 
Checking HTTP proxy: FAIL                                                                                                                                                                      
[Composer\Downloader\TransportException] Connecting to a secure proxy using curl is not supported on PHP versions below 7.3.0.                                                                 
Checking github.com rate limit: FAIL                                                                                                                                                           
[Composer\Downloader\TransportException] Connecting to a secure proxy using curl is not supported on PHP versions below 7.3.0.                                                                 
Checking disk free space: OK                                                                                                                                                                   
Checking pubkeys:                                                                                                                                                                              
Tags Public Key Fingerprint: 57815BA2 7E54DC31 7ECC7CC5 573090D0  87719BA6 8F3BB723 4E5D42D0 84A14642                                                                                          
Dev Public Key Fingerprint: 4AC45767 E5EC2265 2F0C1167 CBBB8A2B  0C708369 153E328C AD90147D AFE50952                                                                                           
OK                                                                                                                                                                                             
Checking composer version: FAIL
[Composer\Downloader\TransportException] Connecting to a secure proxy using curl is not supported on PHP versions below 7.3.0.
Composer version: 2.2.2
PHP version: 7.3.33
PHP binary path: /usr/bin/php
OpenSSL version: OpenSSL 1.0.2k  26 Jan 2017
cURL version: 7.29.0 libz 1.2.7 ssl NSS/3.53.1
zip: extension present, unzip present, 7-Zip not available

Can anyone shed some light on this? I'm dead in the water on builds.

Thanks

CentOS 7, Behind Corporate proxy

Though Composer 2.2 supports PHP 7.2 cURL 7.52 is required. CentOS 7 uses cURL 7.29. Abandoned attempting to use Composer 2.2 to avoid a cURL update on CentOS 7