Hi baksovic and welcome to the Mattermost forums!
With regards to your code:
IncomingWebhookRequest payload = new IncomingWebhookRequest();
payload.setUsername(status.getBotName());
payload.setIconUrl(status.getIcon());
payload.setText(message);
What’s the value of status.getIcon() and can you confirm that the setting to allow changing the profile picture for integrations in the system console is set to true (Integrations → Integrations Management):
What Mattermost server version did you use before you upgraded to 7.5.1?