Client cannot access a subdomain, even though I can

So I set up the client’s domain subdomain to a droplet, which serves as their “backend”. I can access the website fine on admin.clientdomain.com, on mobile, browsers and different browsers or computers. The DNS is handled by digital ocean, and I have confirmed this is working.

When the client attempts to access the subdomain on a safari browser (mac computer), it just reroutes to the main domain. When giving them the IP of the droplet, it just loads a white screen. The droplet has a Wordpress site from the marketplace loaded on it.

The site is also https encrypted with lets-encrypt.

I have

1. Switched off the UFW firewall - no difference
2. Asked the client to clear the cache from their browser / try different browsers - no difference
3. Ran a traceroute from my side to the subdomain, which looks like its working fine.

The website is the default Wordpress one from the marketplace, I have the default apache2 conf, and in /var/html/.htaccess I have this (to redirect to the admin panel, as this is used as a CMS).

RedirectMatch ^/$ /wp-admin

λ tracert admin.vetyogi.com

Tracing route to admin.vetyogi.com [209.97.137.10]
over a maximum of 30 hops:

  1    11 ms     5 ms     6 ms  testwifi.here [192.168.86.1]
  2    17 ms    22 ms    38 ms  10.13.144.1
  3    57 ms    25 ms    18 ms  lutn-core-2b-xe-013-0.network.virginmedia.net [62.252.71.89]
  4    21 ms    24 ms    25 ms  lutn-core-2a-ae1-0.network.virginmedia.net [62.252.64.153]
  5     *        *        *     Request timed out.
  6    28 ms    16 ms    29 ms  m686-mp2.cvx1-b.lis.dial.ntli.net [62.254.42.174]
  7     *        *        *     Request timed out.
  8    18 ms    21 ms    19 ms  uk-lon01b-ri1-ae-25-0.aorta.net [84.116.136.102]
  9    22 ms    20 ms    26 ms  ldn-b1-link.telia.net [213.248.84.25]
 10     *       21 ms     *     ldn-bb4-link.telia.net [62.115.121.28]
 11    21 ms    20 ms    16 ms  ldn-b4-link.telia.net [62.115.134.139]
 12    29 ms    19 ms    18 ms  digitalocean-ic-306494-ldn-b3.c.telia.net [62.115.44.250]
 13     *        *        *     Request timed out.
 14     *        *        *     Request timed out.
 15    27 ms    19 ms     *     209.97.137.10
 16    19 ms    20 ms    16 ms  209.97.137.10

Trace complete.

I’m running out of ideas, besides it being an issue with the client’s ISP.