Entitlement to compensation for posts in case of occupational injury?
Your employer is responsible for ensuring that you have a good working environment and that you are not injured at work. Of course, sometimes it can be difficult to determine the cause of an injury, and your employer may say that the heel spur may have been partly caused by something you do in your spare time, and that's why they only want to pay half the cost. But ask your manager what they base this on and check with HR if there is a policy on this. You probably also have a safety representative at your workplace who can support you, so contact them too.
If you have not already done so, contact your occupational health service. They can work with your employer to review your work environment and see if there are ways to adapt your work tasks so that you do not have to walk and stand so much, at least now during the acute phase of the heel spur. The employer should also carry out a risk assessment of your work tasks, and take measures to minimize the risks, so that you do not become ill or injured from your work.