Access to Rycroft Way is via Chesnut Road (no middle 't' !) : -
https://www.google.com/maps/@51.5910871,-0.069554,3a,16.8y,81.95h,95.42t/data=!3m6!1e1!3m4!1sBHjrvhN8Fti33iSrI3EmvA!2e0!7i16384!8i8192?authuser=0&entry=ttu
Note the large sign with the parking restrictions and also, at the bottom, when the next event is. There is no other motor vehicle access to Rycroft Way, it is all one-way streets.

So unless that sign did not have the date of the next event, your friend looks bang-to-rights.

Well, if you've now paid, there is nothing more we can advise you on. Paying closes off the adjudication appeal option.

The usual grudging acceptance of representations, but hey, well done !

I have to say, having now seen the advance warning sign, that you're likely to struggle overturning this PCN.

Did you look at the sign by the bay which defines the restrictions for the bay ?

None of your reps refutes the requirement for vehicles using the bay for loading to be goods vehicles.  Looking at your photos, your vehicle is a passenger car so you will struggle to overturn the PCN.

Sometimes the PCN can contain a fatal error of content, so if you post the back of it, we can have a loot=k.  The front looks OK, however.

The PCN is misleading in the section "How to challenge".

It states in the 3rd paragraph: -

"If challenges against the PCN are received at the specified address before the NTO is served they will be considered; however, once an NTO is served, any further representations must be made in the form and manner and at the time specified in the NTO"

The Civil Enforcement of Road Traffic Contraventions (Representations and Appeals) (England) Regulations 2022 state, (in Chapter 1)

Information to be included in regulation 9 penalty charge notices and enforcement notices
Information about right to make representations or appeal to be included in regulation 9 penalty charge notices and enforcement notices
3.—(1) A regulation 9 penalty charge notice must include the following information—

(a)that a person on whom a notice to owner is served may, in accordance with these Regulations, make representations to the enforcement authority against the penalty charge and, if those representations are rejected, appeal to an adjudicator;
(b)that if, before a notice to owner is served, representations against the penalty charge are received at such address as may be specified in the notice for the purpose those representations will be considered by the enforcement authority;
(c)that if a notice to owner is served despite the representations mentioned in sub-paragraph (b), representations against the penalty charge must be made to the enforcement authority in the form and manner and at the time specified in the notice to owner.

I have marked in bold the relevant item of mandatory information. You can see that Gloucester, for reasons only known to themselves, have cast aside this sentence and put in their own which has a different meaning. They refer to "further representations" thus implying that if you have already submitted a representation, (your informal challenge) and are happy with it and have no more things to add, that there is no need to submit any representations against the Notice to Owner.  This is highly misleading, because it is essential that a Notice to Owner is either paid or representations made; doing nothing is not an option.

For me, this is a procedural impropriety in that the information mandated to be included has not been included in the PCN.

From what you've said, this was a papers-based adjudication, not a hearing with the adjudicator, (most are done over the phone nowadays).  Is this the case ?  Papers-based adjudications are absolutely NOT recommended by this forum.