Can you please paraphrase the phrases between asterisk?

Question

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All disputes which may emerge in the implementation of this Agreement shall first be settled by the PARTIES by means of consultations and negotiations within 7 (seven) calendar days *after the receival of the notification letter concerning the dispute by either party*.

Answer 1

of the receipt, by either party, of a letter notifying the party of the dispute.

Answer 2

If more than two parties are involved, it would be better to write the following:
*after all parties concerned have received the notification letter concerning the dispute*

If only two parties are involved in this agreement, then use:
*after both parties concerned have received the notification etc..*
You cannot use "either" because it means that one or the other of two parties would not have received the notification and therefore could not negotiate.