Error E2121 – Manual Numbering Not Allowed

When you receive the following error message :

E2121 - ECE_SOAPFaultResponse: We received an error response from the server: FaultCode: Client String.....: You may not enter numbers manually. If you want to enter numbers manually, please activate Manual Nos. in No. Series AA-INV. detail: [string: You may not enter numbers manually. If you want to enter numbers manually, please activate Manual Nos. in No. Series AA-INV. Attributes: xmlns = "http://schemas.microsoft.com/2003/10/Serialization/"] , Data sent: <soap:Body><CreateMultiple xmlns="urn:microsoft-dynamics-schemas/page/salesinvoice"><SalesInvoice_List><SalesInvoice><No>LV00001</No><Sell_to_Customer_No>1234</Sell_to_Customer_No><Your_Reference>0Q0Q5000002knsbKAA</Your_Reference><External_Document_No/><Stripe_ID/><SalesLines><Sales_Invoice_Line><Type>G_L_Account</Type><No>1041</No><Quantity>1.000000</Quantity><Unit_Price>100.00</Unit_Price><Shortcut_Dimension_1_Code>S10</Shortcut_Dimension_1_Code><Shortcut_Dimension_2_Code/><Description>Discounts</Description></Sales_Invoice_Line></SalesLines></SalesInvoice></SalesInvoice_List></CreateMultiple>
</soap:Body>

It means that the system is trying to create a Sales Invoice using a manually defined number (e.g., <No>LV00001</No>), but the No. Series assigned (AA-INV) does not allow manual number entry. Business Central or NAV expects to auto-generate the number instead. 

You have two options to resolve this:

1. Remove the <No> field from your request payload.
    - Business Central or NAV will then auto-assign the next available number from the 'AA-INV' series.

2. Enable Manual Numbering in Business Central or NAV (requires admin access):
    - Go to 'No. Series' in BC.
    - Locate the 'AA-INV' line.
    - Tick the checkbox for 'Manual Nos.'

Unless there's a business requirement to control invoice numbers externally (e.g., syncing with Salesforce or another system), we recommend using Business Central's or NAV's auto-numbering for consistency and to avoid duplicate or conflicting values.
 
 If you must set your own numbers, coordinate with the BC administrator to ensure proper setup of the No. Series.