When adding a cost (fixed or one-off item), click Distribute across clients. Select the clients you want to distribute across and specify a percentage or a fixed amount per client.
Senly registers the split cost as separate lines per client in the client finances, so your profit-per-client remains accurate.
Example: a shared Canva Pro license of €30/month split across 6 clients of €5 each. In each client overview you see €5 client cost; in Finance → Other you see the total €30 as one item.