MultiplierFactorNumeric serializes BaseAmount instead of the percentage factor

[Picaland]

Issue Description
Hi! I noticed that in the current release, NumNum\UBL\AllowanceCharge::xmlSerialize() writes the BaseAmount value into cbc:MultiplierFactorNumeric whenever the multiplier is set. This produces PEPPOL validation errors
(R040/R042) because the field should contain a factor such as 0.10 or 10, not the base amount (e.g. 15.76).

Steps to Reproduce

1. Create an AllowanceCharge instance with

     (new AllowanceCharge())
         ->setChargeIndicator(false)
         ->setBaseAmount(15.76)
         ->setAmount(1.59)
         ->setMultiplierFactorNumeric(0.0997);

2. Serialize it via the UBL invoice generator.

Expected Result
The XML contains cbc:MultiplierFactorNumeric0.0997</cbc:MultiplierFactorNumeric> (or 9.97 depending on convention), matching the PEPPOL requirement.

Actual Result
The generated XML contains cbc:MultiplierFactorNumeric15.76</cbc:MultiplierFactorNumeric>—the base amount value—triggering PEPPOL validation failures such as:

[PEPPOL-EN16931-R040] Allowance/charge amount must equal base amount * percentage/100
[PEPPOL-EN16931-R042] Allowance/charge percentage MUST be provided when allowance/charge base amount is provided.

Suggestion
In AllowanceCharge::xmlSerialize(), replace:

Schema::CBC . 'MultiplierFactorNumeric' => NumberFormatter::format($this->baseAmount)

with:

Schema::CBC . 'MultiplierFactorNumeric' => NumberFormatter::format($this->multiplierFactorNumeric)

(or the equivalent using the getter), so the correct factor is written.

Let me know if you need a full reproducer—happy to help!

[mircobabini]

Nice one! Worth a fix.

[mircobabini]

Is this the PR patching this issue?