I suppose it depends on what you call "proof". Ex-Israeli PM Naftali Bennet, who was an involved, has said that the two sides were in agreement.
Ex-German c=Chancellor Gerhard Schroeder also stipulated that a deal had been reached. https://www.intellinews.com/former-german-leader-schroeder-divulges-more-detail-on-thwarted-russia-ukraine-peace-deal-297990/
Ukrainian negotiator Davyd Arakhamia also confirmed that a deal was on the table, as did Turkish Foreign Minister Mevlut Cavusoglu.
The Ukrainians were ready to sign, to give up NATO membership in return for peace and sovereignty.
But the strongest indication that a deal was imminent came when Boris Johnson “parachuted” unexpectedly into Kiev to squash the deal:
Ukrayinska Pravda (Ukrainian Pravda), reported that Johnson arrived suddenly, “without warning” on April 9, swooping down like some perverse deus ex machina to kill the infant peace deal in its crib.
A close associate of Zelensky described Johnson’s meeting with the Ukrainian President as follows:
“Johnson brought two simple messages to Kyiv: Putin is a war criminal, he should be suppressed, not negotiated with. And secondly, if you are ready to sign any agreements on guarantees with him, then we are not”.
The UP article continues:
Johnson’s position was that the collective West, which back in February had suggested Zelenskyy should surrender and flee, now felt that Putin was not really as powerful as they had previously imagined.
After Johnson’s intervention, according to the article, there was no chance of peace talks progressing.
[Source: Ukrayenska Pravda (UP)]
