(Reuters) -SAP, Europe's largest software provider, offered to buy accounting software firm BlackLine ( BL ) for nearly $4.5 billion in June but was rebuffed and is now considering whether to pursue the company again, according to a copy of the offer letter reviewed by Reuters and a person familiar with the matter.  

The German software giant, which is working with JPMorgan on the deal, submitted a formal, non-public offer of $66 per share on June 18, but BlackLine ( BL ) wasn't interested in a deal and rejected the advance, according to the letter and person familiar with the talks. The offer represented a 31% premium to the 60-day average price of $50.50. In the offer letter, SAP said it doesn't need outside financing to close the deal.  

Private equity firm Clearlake Capital holds nearly 9% of BlackLine's ( BL ) shares and would have a say in a potential sale as a large shareholder. The Vanguard Group and BlackRock are other top shareholders through their fund families. 

SAP is now weighing whether it wants to reopen negotiations, although nothing's been decided and it hasn't sent another formal offer, according to the person familiar with the matter. They asked not to be identified since the discussions are private.

SAP, JPMorgan and Clearlake declined to comment. BlackLine ( BL ) and Morgan Stanley did not immediately respond to requests for comment.

Los Angeles-based BlackLine ( BL ) provides cloud-based software that helps companies automate and manage complex financial and accounting processes. Its products are designed to modernize tasks traditionally done on spreadsheets, reducing errors and increasing efficiency for corporate finance departments.

BlackLine ( BL ) and SAP have a long-standing partnership; SAP sells BlackLine's ( BL ) solutions to its customers. The agreement accounts for nearly 30% of BlackLine's ( BL ) annual revenue, according to company disclosures.

SAP's Chief Financial Officer Dominik Asam and Chief Corporate Development and Investment Officer Georg Kniese said buying BlackLine ( BL ) represents a "logical extension of the long standing partnership" between the two companies, according to the offer letter addressed to BlackLine ( BL ) co-CEOs Theresa Tucker and Owen Ryan.

The offer came as Tucker, who founded BlackLine ( BL ) and stepped down earlier this month, was preparing to hand over the reins to Ryan, who also serves as chairman.

An acquisition of BlackLine ( BL ) would significantly bolster SAP's cloud-based financial software suite as it competes with rivals like Oracle and Workday.

BlackLine's ( BL ) financial automation software, already tightly integrated with SAP, helps companies clean up financial records before migrating to new platforms. BlackLine ( BL ) could help SAP, which has struggled to quickly migrate customer data to its newer HANA cloud platform, potentially boost HANA adoption by simplifying that process.