How can we improve WHMCS?

You should not change the currency of a client. WHMCS doesn't store currency value for invoices therefore it also doesn't update pricing. It simply changes currency prefix and suffix.

For example let's say that you have a client with an invoice of 100 INR. As soon as you change to EUR, the invoice becomes 100 EUR but in reality 100 INR are equal to 1.41 EUR so it's a disaster.

There are modules in the Marketplace that allow you to freely change the currency of a client without messing up with existing invoices.

Here's what we've been doing - which you could automate with some database queries if you often need to switch currencies. (Perhaps one of those modules does something similar - I never checked.)

* Set the client's profile to Inactive or Closed (or whatever status you don't send e-mails to.)
* Change their e-mail from [email protected] to [email protected]/USD (or whatever currency it is.)
* Create a new profile for the [email protected] using the new currency.
* Move products from the old to the new client.
* Update products pricing to use their new currency.

This way their old invoices remain properly stored in the old currency while new invoices are generated in the new currency. You can switch back and forth whenever you want, without compromising the invoices.

Two shortcomings of this approach: 1) The client cannot access the invoices in the inactive account, unless you teach them to login with /USD to see the old invoices. 2) It only fixes the currency issue. Other changes (like name and address) will still change whenever the customer changes them. (Which is illegal in most places.)

i request this before 3 months, please like my request too, to apply this update urgently.

It's not a bug. This is how WHMCS handles currency change. Basically you should not allow clients to change their currency since this value is crucial and not intended to change. There are 2 possible solution:

• Create a new account for your client with his/her new currency setting and move all domains/products from the old one. Of course keep the old account still alive as a reference
• There are modules that allow you to "cache" currency prefix and suffix so that you can freely change this value for every client
  

Actually I disagree. If you are not supposed to change your customer currency and it's a bug like you mentioned, then it would not be there in the first place. WHMCS would not have this option if what you said is true. The option is there because its something users requested and WHMCS added it. The bug here is that WHMCS changes the currency symbol on all the invoices and transactions. It should only change the new ones, not past ones. This is the bug people complain, they don't complain about the feature that changes the currency in the customer account (as that works) but how its changing it.
I like Linus Torwalds quote here. If enough people are using or rely on a bug then its not a bug anymore, it's a feature. Changing currency is something that people want and request as you can see here for the simple reason that a customer may want to change his currency. A simple example of this is someone moving from Europe to the US and now wants his invoices in USD instead of Euros or the other way around. WHMCS can change currency without issues in the customer account, the bug here is that it also changes them for past transactions and invoices because all it does its update the currency symbol in the SQL database. This is actually amazingly dumb to fix. All they need to check is the time stamp or date and freeze those records so they are not changed when you hit the change currency button. This way the change will apply to new transactions and invoices but not past ones.