'agreed via' is correct and can be used in written English.
You can use it when you are indicating that an agreement was reached through a medium other than in person. For example, "The terms of the contract were agreed via email."
Jarrett acknowledged that he had agreed via radio to work with Martin, but not indefinitely.
She points out that politicians have just agreed, via the most recent UN sustainable development goals decided in New York in September, to eliminate homelessness by 2030.
Pattaramon Chanbua, from Chonburi province, south-east of Bangkok, had agreed via an agent to be a surrogate for the couple's twins, who were born in December, for a fee of £8,850.
The BMA said: "Junior doctors should continue with industrial action until NHS England has confirmed and the BMA has agreed – via the agreed escalation process – that a major unpredictable incident is taking place for a specific Trust.
Robert Pondiscio, former fifth-grade teacher at P.S. 277 in the South Bronx, agreed, via e-mail: The battle over homework is one of those things that differentiates education among the privileged and everyone else.
By late afternoon on Tuesday, Mr. Hatch had said that he would support the bill out of committee, if not necessarily on the Senate floor, after the committee agreed, via a voice vote, to pass his amendment.
Is The Times agreeing, via its "pick," with the notion that the Fed chairmanship is not "a woman's job" and requires "virility"?
In addition, the E.I.R. agrees — via contract or, more often, tacitly — to give the venture capital firm the first shot to invest in an idea.
The list predicts that after Pelosi comes a final speaker ("weepy kumquat") who presides over an era in which Congress loses all remaining capacity to direct the nation's economic affairs beyond sporadically agreeing, via text, to have the nation's bureaucracy just keep doing whatever it was doing before.
Parks assessment districts are geographically-specific areas that agree (via a vote of those within the area) to support ongoing funding for a specific park, usually in the form of a small supplement to property taxes.
Last year, consumers adopted the flash mob concept -- random strangers agreeing via social media to gather and burst into one joyful coordinated action -- as a means to support their local businesses with so-called "cash mobs," where a big rush of customers would coordinate to swarm a nearby small business to boost its sales.
