|Towards more picturesque speech™
A beer I hold for or on my client’s behalf, remains my client’s while I hold it, my client being otherwise occupied with his one-handed push-ups or whatever other prowess or feat of strength it may have come into his mind to demonstrate. I am my client’s agent.
And so to money; amounts I hold for and on your behalf do not correspond to my liabilities to you (except for the uncomfortable ontological fact that holding money for someone, a propos no other contract, still, of necessity generates a liability to repay it). There is a difference, that is to say, between money I owe you, because we have entered some contract for a good or service, and money I hold for you, because some other random, who owed it to you, gave it to me to pass on to you, a propos nothing beyond my general preparedness to act for or on behalf of you, dear friend. And client.
This is a tiresome but important point when understanding the scope of the FCA’s client money rules.
In modern usage, “behalf” is an invariable noun, meaning it has no plural form. In the 15th and 16th century you did see “behalves” but it has fallen out of use, the theory being that the collected persons on whose behalf you are acting are indivisible.