Try not to use hackneyed wording
For example, wording like "please accept our apologies on behalf of the company" or "we apologize...", "we regret that...", "we are very sorry" etc. have long been familiar and boring. They look like formal replies (and often are), so they cause irritation.
But at the same time, words of apology must be said, otherwise it will not be an apology.
Trying to "appeal to pity" also does not always work as expected - the client may perceive it as an element of weakness. Apologies and regrets must be handled with extreme caution and thoughtfulness.
Be more creative. Make it clear that a human being wrote the text and that he or she has a genuine desire (or has tried) to solve the problem.
If the structure of the apology mentions inconveniences, then it is necessary to understand that the inconveniences must really be such. Thus, the need to go to the office across the whole city is an inconvenience, but a late courier or an order delivered late is a specific problem (not an inconvenience). And it is this problem that needs to be described (solved) in the apology letter.
Don't be shy about admitting your mistakes
Use important details, but without dangerous details. The main morocco phone number data message is to show the client the cause of all evil, what led to the problem: a specific employee, a server failure, the actions of partners, etc.
All of this is important so that the client can understand your situation.
But it is important not to overdo it. There is no need to fawn, to press on pity or to share too intimate details. This should be an almost equal dialogue - as if you were telling your partner why you were unable to fulfill your obligations.
Keep your promises
If you promise discounts or bonuses to compensate (make amends for your guilt), then such promises must be fulfilled. If you promise to fix a specific error in the operation of the application/website/personal account, then it really must be fixed.
Otherwise, the blunder may be even bigger. For example, when the client comes back for your services and realizes that you deceived him. Apart from additional negativity, such promises will lead to nothing.
If you can't guarantee that you'll fulfill your obligations, then just don't promise anything.